1. Field of the Invention
The present invention is directed to a method and apparatus for gradient power supply in a magnetic resonance imaging apparatus, for producing a gradient offset current.
2. Description of the Prior Art
U.S. Pat. No. 5,245,287 discloses a gradient power supply for a nuclear magnetic resonance tomography apparatus wherein the gradient coil is operated in a resonant circuit. Fast changes in current can be realized by the resonant operation of the gradient coil; these could not be realized with only a linear gradient amplifier or could be realized therewith with great outlay.
A setting possibility for shim currents is often provided in nuclear magnetic resonant tomography apparatus in order to improve the homogeneity. For example, this can be required before every measurement given high demands. Linear homogeneity terms can thereby be simply set in that a constant offset current is supplied to the gradient coils present for all three spatial directions in addition to the gradient power is predetermined by a sequence controller. This does not seem possible given operation of the gradient coil in a resonant circuit since, of course, the DC current cannot be conducted over a capacitor.